Projector

ABSTRACT

When axes are projected to a reference surface perpendicular in the thickness direction of a liquid crystal layer, a rotational angle φ 0  of an alignment axis of a liquid crystal layer from a reference direction on the reference surface, a rotational angle φ 1  of a transmission axis of an incident-side polarizing plate from the reference direction, a rotational angle φ 2  of a transmission axis of a wire grid element from the reference direction, and a rotational angle φ 3  of a transmission axis of an exit-side polarizing plate from the reference direction satisfy all the equations below: 
       44°≦φ 0 −φ 2 &lt;45° or 45°&lt;φ 0 −φ 2 ≦46°
 
         f 1≦φ 1   ≦f 2,
 
     where
         f1=0.191×φ 2   2 +0.986×φ 2 −14.435 and f2=−0.191×φ 2   2 +0.986×φ 2 +14.435, and       

         g 1≦φ 1   ≦g 2,
 
     where
         g1=0.064×φ 3   3 +0.841×φ 3   3 +1.525×φ 3   3 −1.46 and g2=0.064×φ 3   3 −0.841×φ 3   3 +1.525×φ 3   3 +1.46.

BACKGROUND

1. Technical Field

The present invention relates to a projector.

2. Related Art

Hitherto, a reflection type projector has been known as one of theliquid crystal projectors (for example, see JP-A-2004-46156). Forexample, the reflection type projector includes an illumination opticalsystem, a wire grid element, a reflection type liquid crystal panel, anda projection optical system.

Light emitted from the illumination optical system is incident on aliquid crystal panel via a polarization separating element. The lightincident on the liquid crystal panel is modulated and reflected by theliquid crystal panel. The light reflected by the liquid crystal panel isincident again on the polarization separating element and is separatedinto polarized light for showing an image and polarized light forshowing a reversed image. The projection optical system projects thepolarized light for showing the image to a screen or the like to displaythe image.

In some cases, the reflection type liquid crystal panel is configured toinclude a vertical alignment mode (hereinafter, referred to as a VAmode) liquid crystal layer advantageous to improve a contrast ratio. Inthe VA mode liquid crystal layer, a pretilt is given in a predetermineddirection so as to have an alignment property in many cases. When thepretilt is given in the liquid crystal layer, disclination can beprevented from occurring. However, refractive index anisotropy may occurin the liquid crystal layer when no electric field is applied.

To remove the refractive index anisotropy, an optical compensation platemay be provided in addition to the liquid crystal layer so that therefractive index becomes isotropic. Further, a technique has beensuggested to reduce the refractive index anisotropy of the liquidcrystal layer when no electric field is applied (for example,JP-A-2007-212997). In JP-A-2007-212997, in a liquid crystal panel inwhich a liquid crystal layer is interposed between a pair of substrates,the alignment axis of the liquid crystal layer is different at one andthe other of the pair of substrates.

In the projector, the contrast ratio is expected to be newly improved,and thus the projector with the above-described configuration can beallowed to be improved. For example, in the liquid crystal panel, thealignment axis of the liquid crystal layer may sometimes be deviatedfrom a predetermined direction due to a manufacture error or the like.When the alignment axis of the liquid crystal layer is deviated from thepredetermined direction, a rotational angle between the optical axis ofa polarizing plate, a wire grid element, or the like and the alignmentaxis of the liquid crystal layer may be deviated from a predeterminedrotational angle. As a result, a ratio of the polarized light, which isincluded in the light projected by the projection optical system, forshowing a reverse image may be increased, thereby deteriorating thecontrast ratio of the projected image.

SUMMARY

An advantage of some aspects of the invention is that it provides aprojector capable of preventing a contrast ratio from deteriorating dueto a deviation in a relative rotational angle of the optical axis of anoptical element such as a liquid crystal panel or a wire grid element.

According to an aspect of the invention, there is provided a projectorincluding: an illumination optical system; an incident-side polarizingplate which is disposed at a position at which light emitted from theillumination optical system is incident and through which polarizedlight parallel to a transmission axis passes; a wire grid element whichis disposed at a position at which the light emitted from theillumination optical system and passing through the incident-sidepolarizing plate is incident, through which polarized light parallel toa transmission axis passes, and from which polarized light perpendicularto the transmission axis is reflected; a reflection type liquid crystalpanel which is disposed at a position at which the light emitted fromthe illumination optical system and passing through the wire gridelement is incident; an exit-side polarizing plate which is disposed ata position at which light reflected by the wire grid element in thelight modulated and reflected by the liquid crystal panel and incidenton the wire grid element is incident and through which polarized lightparallel to a transmission axis passes; and a projection optical systemwhich projects the light modulated by the liquid crystal panel andpassing through the exit-side polarizing plate. In regard to analignment axis parallel to a direction, in which a director of a liquidcrystal molecule in a liquid crystal layer of the liquid crystal panelis projected to a surface perpendicular to a thickness direction of theliquid crystal layer, the transmission axis of the incident-sidepolarizing plate and the transmission axis of the wire grid elementwhich are projected to a reference surface perpendicular in thethickness direction of the liquid crystal layer of the liquid crystalpanel, the transmission axis of the exit-side polarizing plate which isprojected to the wire grid element and is further projected to thereference surface, a rotational angle φ₀ of the alignment axis of theliquid crystal layer from a reference direction parallel to thereference surface, a rotational angle φ₁ of the transmission axis of theincident-side polarizing plate from the reference direction, arotational angle φ₂ of the transmission axis of the wire grid elementfrom the reference direction, and a rotational angle φ₃ of thetransmission axis of the exit-side polarizing plate from the referencedirection satisfy all Equations (1) to (3) below:

44°≦φ₀−φ₂<45° or 45°<φ₀−φ₂≦46°  (1)

f1≦φ₁ ≦f2  (2),

where

-   -   f1=0.191×φ₂ ²+0.986×φ₂−14.435 and f2=−0.191×φ₂        ²+0.986×φ₂+14.435, and

g1≦φ₁ ≦g2  (3),

where

-   -   g1=0.064×φ₃ ³+0.841×φ₃ ³+1.525×φ₃ ³−1.46 and g2=0.064×φ₃        ³−0.841×φ₃ ³+1.525φ₃ ³+1.46.

In the projector, the rotational angles φ₀ to φ₃ satisfy all Equations(1) to (3). Since the minimum value of a contrast ratio is 80% or moreof the maximum value, a deterioration in the contrast ratio can besuppressed so that an observer scarcely recognizes the deterioration inthe contrast ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a diagram illustrating the overall configuration of aprojector according to an embodiment.

FIG. 2 is a diagram schematically illustrating the configuration of animage forming system according to the embodiment.

FIG. 3 is a diagram schematically illustrating the configuration of aliquid crystal panel according to the embodiment.

FIG. 4 is a diagram illustrating a first arrangement of optical elementsof the image forming system according to the embodiment.

FIG. 5 is a distribution diagram illustrating a simulation resultobtained by varying the rotational angle of the transmission axis of anincident-side polarizing plate and the rotational angle of thetransmission axis of a wire grid element and examining a variation inthe lightness of light display.

FIG. 6 is a distribution diagram illustrating a simulation resultobtained by varying the rotational angle of the transmission axis of anexit-side polarizing plate and the rotational angle of the transmissionaxis of a wire grid element and examining the lightness of lightdisplay.

FIG. 7 is a diagram illustrating a second arrangement of the opticalelements of the image forming system according to the embodiment.

FIG. 8 is a diagram illustrating a third arrangement of optical elementsof the image forming system according to the embodiment.

FIG. 9 is a diagram illustrating a fourth arrangement of the opticalelements of the image forming system according to the embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, an embodiment of the invention will be described withreference to the drawings. The size or scale of the configuration in thedrawings used for the description may be different from the actual sizeor scale.

FIG. 1 is a diagram illustrating the overall configuration of aprojector according to an embodiment. FIG. 2 is a diagram schematicallyillustrating the configurations of an image forming system and a colorsynthesizing unit according to the embodiment. FIG. 3 is a diagramschematically illustrating the configuration of a liquid crystal panel.

A projector 1 shown in FIG. 1 includes an illumination optical system 2,a blue image forming system 3, a green image forming system 4, a redimage forming system 5, a color synthesizing unit 6, and a projectionoptical system 7.

The illumination optical system 2 can separately emit blue light L1,green light L2, and red light L3. The color image forming systems arearranged so as to have a one-to-one correspondence relationship with therespective light emitted from the illumination optical system 2, andthus can modulate the corresponding color light to form images of therespective colors. The color synthesizing unit 6 can synthesize thelight for showing the images of the three colors formed by the threeimage forming systems. The projection optical system 7 can project thelight synthesized by the color synthesizing unit 6 to a projectionsurface such as a wall or a screen.

The illumination optical system 2 according to this embodiment includesa light source unit 10, an integrator optical system 11, and a colorseparation optical system 12. The light source unit 10 can emit whitelight L which includes the blue light L1 with a wavelength equal to orgreater than 450 nm and less than 495 nm, the green light L2 with awavelength equal to or greater than 495 nm and less than 570 nm, and thered light L3 with a wavelength equal to or greater than 620 nm and lessthan 750 nm. The integrator optical system 11 can uniformalize theilluminance of the white light L emitted from the light source unit 10and align a polarized state. The color separation optical system 12 canseparate the white light L emitted from the integrator optical system 11into the blue light L1, the green light L2, and the red light L3.

The light source unit 10 according to this embodiment includes a lightsource lamp 13 that emits white light and a reflecting mirror 14 thathas a reflection surface with a rotation paraboloid shape. The whitelight emitted from the light source lamp 13 is reflected in onedirection from the reflecting mirror 14 and becomes a substantiallyparallel light flux. The light source lamp 13 is configured by, forexample, a metal halide lamp, a xenon lamp, a high-pressure mercurylamp, or a halogen lamp. The light is incident on the integrator opticalsystem 11 by the reflecting mirror 14. The reflecting mirror 14 may havea reflection surface with a rotation elliptical shape. In this case, aparallelizing lens may be used to parallelize the white light exitingfrom the reflecting mirror.

The integrator optical system 11 according to this embodiment includes afirst lens array 15, a second lens array 16, a polarization convertingelement 17, and a superimposing lens 18.

The first lens array 15 and the second lens array 16 each have aplurality of microlenses arranged two-dimensionally on a planeperpendicular to the optical axis of the light source unit 10. Themicrolenses of the first lens array 15 are arranged to have a one-to-onecorrespondence relationship with the microlenses of the second lensarray 16. The plurality of microlenses have a substantially rectangularshape, which is similar to that of an illumination region 35 of a liquidcrystal panel 27 (see FIG. 2) described below, on the planeperpendicular to the optical axis of the light source unit 10.

The polarization converting element 17 includes a plurality of cellsarranged two-dimensionally on the plane perpendicular to the opticalaxis of the light source unit 10. The cells of the polarizationconverting element 17 are arranged to have a one-to-one correspondencerelationship with the microlenses of the second lens array 16. Theplurality of cells each have a polarization beam splitter film(hereinafter, referred to as a PBS film), a ½ phase plate, and areflecting mirror.

The white light L incident on the first lens array 15 from the lightsource unit 10 is condensed into the respective microlenses and isdivided into a plurality of partial light fluxes. The partial light fluxexiting from each microlens of the first lens array 15 is imaged in themicrolens of the second lens array 16 corresponding to this microlens toform a secondary light source in the microlens. The partial light fluxexiting from each microlens of the second lens array 16 is incident onthe cell of the polarization converting element 17 corresponding to thismicrolens.

The polarization converting element 17 is disposed in a light pathbetween the second lens array 16 and the superimposing lens 18. Thepartial light flux incident on each cell of the polarization convertingelement 17 is separated into P-polarized light and S-polarized light forthe PBS film. One polarized light flux separated from the partial lightflux is reflected from the reflecting mirror, and then passes throughthe ½ phase plate so that the polarized state can be aligned with theother polarized light. In this embodiment, each cell of the polarizationconverting element 17 can align the polarized state of the partial lightflux incident on each cell to the P-polarized light with respect to awire grid element 26 (which is described later) of each image formingsystem. The plurality of partial light fluxes emitted from the pluralityof cells of the polarization converting element 17 are refracted by thesuperimposing lens 18, and thus are superimposed on a pixel region 35 ofthe liquid crystal panel 27 of each image forming system.

The color separation optical system 12 includes a first dichroic mirror20, a second dichroic mirror 21, a third dichroic mirror 22, a firstreflecting mirror 23, and a second reflecting mirror 24. The firstdichroic mirror 20 has a property of transmitting the red light L3 andreflecting the green light L2 and the blue light L1. The second dichroicmirror 21 has a property of reflecting the red light L3 and transmittingthe green light L2 and the blue light L1. The third dichroic mirror 22has a property of reflecting the green light L2 and transmitting theblue light L1. The first dichroic mirror 20 and the second dichroicmirror 21 are almost perpendicular to each other and are disposed toform nearly 45° with the optical axis of the integrator optical system11.

In the white light L incident on the color separation optical system 12,the red light L3 is reflected from the second dichroic mirror 21, isreflected from the first reflection mirror 23, and then is incident onthe red image forming system 5. In the white light L incident on thecolor separation optical system 12, the blue light L1 and the greenlight L2 are reflected from the first dichroic mirror 20, are reflectedfrom a second reflection mirror 24, and then is incident on the thirddichroic mirror 22. The green light L2 incident on the third dichroicmirror 22 is reflected from the third dichroic mirror 22 and is incidenton the green image forming system 4. The blue light L1 incident on thethird dichroic mirror 22 passes through the third dichroic mirror 22 andis incident on the blue image forming system 3.

The blue image forming system 3, the green image forming system 4, andthe red image forming system 5 have almost the same configuration. Inthis embodiment, the configuration of the green image forming system 4will be described as a representative example of the image formingsystems. The green image forming system 4 shown in FIG. 2 includes anincident-side polarizing plate 25, a wire grid element 26, a liquidcrystal panel 27, and an exit-side polarizing plate 28.

The green light L2 emitted from the color separation optical system 12is incident on the incident-side polarizing plate 25. The incident-sidepolarizing plate 25 has a property of transmitting linearly polarizedlight parallel to a transmission axis 29 and absorbing linearlypolarized light parallel to an absorption axis 30 perpendicular to thetransmission axis 29. In the green light L2 incident on theincident-side polarizing plate 25 from the color separation opticalsystem 12, the green light L2 passing through the incident-sidepolarizing plate 25 is incident on the wire grid element 26.

The wire grid element 26 is disposed to be inclined by an angle ofnearly 45° with respect to the travel direction of the green light L2incident on the wire grid element 26 from the incident-side polarizingplate 25. The wire grid element 26 according to this embodiment includesa dielectric layer 31 made of glass or the like and a plurality of metalwires 32 formed on the surface or a surface layer of the dielectriclayer 31 and extending parallel to each other.

The wire grid element 26 has a property of transmitting the linearlypolarized light perpendicular to the metal wires 32 and the linearlypolarized light parallel to the metal wires 32. In other words, in thewire grid element 26, a transmission axis 33 is perpendicular to themetal wires 32 and a reflection axis 34 is parallel to the metal wires32. In the green light L2 incident on the wire grid element 26 from theincident-side polarizing plate 25, the green light L2 passing throughthe wire grid element 26 is incident on the liquid crystal panel 27.

The liquid crystal panel 27 includes a plurality of pixels P arrangedtwo-dimensionally. In this embodiment, one of two arrangement directionsof the pixels P is almost parallel to an X direction and the other ofthe two arrangement directions of the pixels P is almost parallel to a Ydirection. In the following description, a direction perpendicular toeither of the two arrangement directions of the pixels in the liquidcrystal panel is the normal direction of the liquid crystal panel. Thenormal direction of the liquid crystal panel is almost parallel to thethickness direction of the liquid crystal layer of the liquid crystalpanel.

The green light L2 passing through the wire grid element 26 is incidenton a region (the pixel region 35) where the plurality of pixels P arearranged. The liquid crystal panel 27 is disposes such that thethickness direction of the liquid crystal layer 42 (see FIG. 3) isalmost parallel to the travel direction of the green light L2 incidenton the liquid crystal panel 27 from the wire grid element 26.

The green light L2 incident on the liquid crystal panel 27 from the wiregrid element 26 is modulated and reflected by the liquid crystal panel27, and thus the travel direction of the green light L2 is changed bynearly 180° from the travel direction of the green light L2 before thegreen light L2 is incident on the liquid crystal panel 27. The greenlight L2 exiting from the liquid crystal panel 27 is incident again onthe wire grid element 26.

In the green light L2 incident on the wire grid element 26 from theliquid crystal panel 27, the green light L2 reflected from the wire gridelement 26 is incident on the exit-side polarizing plate 28. Theexit-side polarizing plate 28 has a property of transmitting thelinearly polarized light parallel to a transmission axis 36 andabsorbing the linearly polarized light parallel an absorption axis 37perpendicular to the transmission axis 36. In the green light L2incident on the exit-side polarizing plate 28 from the wire grid element26, the green light L2 passing through the exit-side polarizing plate 28is incident on the color synthesizing unit 6.

As shown in FIG. 3, the liquid crystal panel 27 includes an elementsubstrate 40, a counter substrate 41, a liquid crystal layer 42, and acompensating plate 43. The element substrate 40 is disposed to face thecounter substrate 41. The liquid crystal layer 42 is sealed between theelement substrate 40 and the counter substrate 41. The compensatingplate 43 is disposed to be opposite to the liquid crystal layer 42 withrespect to the counter substrate 41.

The green light L2 passing through the wire grid element 26 and incidenton the liquid crystal panel 27 is incident on the compensating plate 43,passes through the counter substrate 41, is incident on the liquidcrystal layer 42, and is reflected from the element substrate 40 to bereversed. The green light L2 is modulated while passing through theliquid crystal layer 42, exits from the liquid crystal layer 42, isincident on the counter substrate 41, passes through the compensatingplate 43, and exits from the liquid crystal panel 27.

The element substrate 40 is configured by a silicon substrate or a glasssubstrate as a base substrate. When the element substrate 40 is formedof a silicon substrate, a so-called LCOS (Liquid Crystal On Silicon) isconfigured. The element substrate 40 includes a plurality of gate lines44, a plurality of source lines 45, a plurality of thin film transistors(hereinafter, referred to as TFTs 46), and pixel electrodes 47.

The plurality of gate lines 44 extend to be parallel to each other. Theplurality of source lines 45 extends to be parallel to each other. Thegate lines 44 are perpendicular to the source lines 45. The TFT 46 isdisposed at each of the intersections between the gate lines 44 and thesource lines 45. The gate line 44 is electrically connected to a gateelectrode of the TFT 46. The source line 45 is electrically connected toa source region of the TFT 46.

Each pixel P of the liquid crystal panel 27 corresponds to a portionsurrounded by the gate lines 44 and the source lines 45. The pixelelectrodes 47 are disposed so as to have a one-to-one correspondencerelationship with the pixels P. In this embodiment, the pixel electrode47 is made of a metal material and also functions as a mirror surfacereflecting plate. FIG. 3 schematically shows the ground side of thepixel electrodes 47 by notching the pixel electrodes 47. In effect, thepixel electrodes 47 are configured to cover the gate lines 44, thesource lines 45, and the TFTs 46 with a flattened layer or a insulationlayer interposed therebetween, thereby improving an aperture ratio ofthe pixel P. The pixel electrode 47 is electrically connected to a drainregion of the TFT 46. An alignment film (not shown) is disposed to coverthe pixel electrode 47.

The counter substrate 41 is configured by a substrate, such as a glasssubstrate, having a transmission property as a base substrate. A commonelectrode made of a transparent conductive material such as indium tinoxide is disposed in the counter substrate 41 on the side of the liquidcrystal layer 42. An alignment film is disposed in the common electrodeon the side of the liquid crystal layer 42. The alignment film disposedin the element substrate 40 or the counter substrate 41 is an inorganicalignment film formed by, for example, an oblique evaporation method.

The liquid crystal layer 42 is configured by a VA mode liquid crystallayer. A cell gap between the element substrate 40 and the countersubstrate 41 is, for example, about 2.0 μm. The liquid crystal materialis sealed in the cell gap to form the liquid crystal layer 42. Theliquid crystal material has negative dielectric constant anisotropy andbirefringence Δn of, for example, 0.12.

The alignment property of the liquid crystal layer 42 is defined by thealignment film when no electric field is applied. A director of a liquidcrystal molecule 48 included in the liquid crystal layer 42 has an angle(pretilt angle θ) of, for example, about 87°, which is formed by thethickness direction of the liquid crystal layer 42 and the directionparallel to the surface (the substrate surface of the element substrate40) perpendicular to the thickness direction of the liquid crystal layer42. An alignment axis 49 of the liquid crystal layer 42 is parallel to avector obtained by orthogonally projecting the director of the liquidcrystal molecule 48 to the plane perpendicular to the thicknessdirection of the liquid crystal layer 42.

The compensating plate 43 is disposed so as to cancel the dielectricconstant anisotropy of the liquid crystal layer 42 by the pretilt andremove the dielectric constant anisotropy of both the liquid crystallayer 42 and the compensating plate 43 when no electric field isapplied. The compensating plate 43 is formed of, for example, a negativeC-plate. The compensating plate 43 is disposed so as to be rotatedaround a rotational axis from a position perpendicular to the thicknessdirection of the liquid crystal layer 42 on the assumption that adirection parallel to the axis, at which the alignment axis 49 isrotated by nearly 135° when viewed from the thickness direction of theliquid crystal layer 42, is the rotational axis. The compensating plate43 is disposed to be inclined by nearly 4.5° with respect to a surfaceperpendicular to the thickness direction of the liquid crystal layer 42.

When a selection pulse is supplied to the gate line 44 in the liquidcrystal panel 27 with the above-described configuration, the TFTs 46connected to the gate line 44 are turned on. When the TFTs 46 are turnedon, a source signal corresponding to a gray scale value of each pixel Pis supplied to the source line 45 and the source signal is supplied tothe pixel electrodes 47 via the TFTs 46. When the source signal issupplied to the pixel electrodes 47, an electric field is appliedbetween the pixel electrodes 47 and the common electrode and thedirector of the liquid crystal molecules 48 of the liquid crystal layer42 is changed in each pixel P in accordance with the electric field. Thepolarization state of the green light L2 incident on the pixel P ischanged in accordance with the azimuth angle of the director of theliquid crystal molecules 48 of the liquid crystal layer 42 in this pixelP.

In this embodiment, when the electric field is not applied to the liquidcrystal layer 42 in one arbitrary pixel P, the polarization state of thegreen light L2 incident on this pixel P is not nearly changed and thegreen light L2 exits in a P polarization state. When the electric fieldis applied to the liquid crystal layer 42 in one arbitrary pixel P, thegreen light L2 incident on this pixel P is changed from the Ppolarization to the S polarization with respect to the wire grid element26 at a ratio corresponding to the gray scale value defined in imagedata. That is, in the green light L2 passing through the liquid crystallayer 42, the S-polarized light with respect to the wire grid element 26is light for showing an image.

Referring back to FIG. 2, the color synthesizing unit 6 is configured bya dichroic prism or the like. The dichroic prism has a configuration inwhich four triangular prisms are adhered to each other. The surfaces towhich the respective triangular prisms are adhered are the innersurfaces of the dichroic prism. In the dichroic prism, a wavelengthselection film having a property of reflecting the red light L3 andtransmitting the green light L2 and the blue light L1 and a wavelengthselection film having a property of reflecting the blue light L1 and thetransmitting the green light L2 and the red light L3 are perpendicularto each other to form the inner surfaces.

The green light L2 incident on the dichroic prism passes through thewavelength selection films and exits without any change. The blue lightL1 and the red light L3 incident on the dichroic prism be selectivelyreflected from or pass through the wave selection films and exit in thesame direction as the exit direction of the green light L2. In this way,the three-color light is superimposed and synthesized to formsynthesized light for showing a full-color image, and then is incidenton the projection optical system 7. The projection optical system 7forms an image of the synthesized light on a projection surface todisplay the full-color image on the projection surface.

However, the alignment axis 49 of the liquid crystal layer 42 of theabove-described liquid crystal panel 27 may be deviated from apredetermined direction due to an error or the like when the alignmentfilm is formed. For example, when a plurality of liquid crystal panelsare manufactured using a substrate broader the liquid crystal panel, anorganic alignment film is formed on the substrate by an obliqueevaporation method or the like in some cases. In this case, in theplurality of liquid crystal panels manufactured using the substrate, thedirection of the alignment axis of the liquid crystal layer is irregularsince an evaporation angle is changed depending on the position of theliquid crystal layer on the substrate. As the deviation amount (error)increases from a predetermined direction of the alignment axis of theliquid crystal layer, the deviation amount increases from apredetermined direction of the polarization direction of the lightemitted from the liquid crystal layer. As a result, the contrast ratioof a projected image may deteriorate due to an increase in a ratio ofthe light, which is included in the light reflected and projected fromthe wire grid element, for showing a reversed image.

In the projector 1 according to this embodiment, the direction of anoptical axis of an optical element forming each image forming system isset in a manner described below. Therefore, it is possible to preventthe contrast ratio from deteriorating due to the deviation of thealignment axis 49 from a predetermined direction.

FIG. 4 is a diagram illustrating a first arrangement of optical elementsof an image forming system according to this embodiment. FIG. 4 showsthe optical elements of the green image forming system 4 which is arepresentative of the three image forming systems. Specifically, FIG. 4is a plan view illustrating the directions of the transmission axis 29of the incident-side polarizing plate 25, the transmission axis 33 ofthe wire grid element 26, the alignment axis 49 of the liquid crystalpanel 27, and the transmission axis 36 of the exit-side polarizing plate28 when viewed from the incident-side polarizing plate 25 in the normaldirection of the liquid crystal panel 27.

The transmission axis 36 of the exit-side polarizing plate 28 in FIG. 4is illustrated by projecting the transmission axis 36 to the surface ofthe wire grid element 26 in a direction parallel to the travel direction(the X direction) of the green light L2 reflected from the wire gridelement 26 and traveling toward the exit-side polarizing plate 28 and byfurther projecting the transmission axis 36 projected to the wire gridelement 26 to the pixel region 35 of the liquid crystal panel 27 in adirection parallel to the normal direction of the liquid crystal panel27. The same is applied to the blue image forming system 3 and the redimage forming system 5.

In this embodiment, a rotational angle of an optical axis of eachoptical element is a rotational angle measured from a referencedirection within plane perpendicular to the normal direction of theliquid crystal panel to the axis of a target, when a counterclockwisedirection is a positive direction. In this embodiment, the referencedirection is one (the X direction) of the two arrangement directions ofthe pixels P in the liquid crystal panel 27. Further, angles equal to orgreater than 180° and less than 360° is treated as angles equal to orgreater than −180° and less than 0°.

In the first arrangement, the alignment axis 49 of the liquid crystallayer 42 is present between the range equal to or greater than 45° andless than 90° and the range equal to or greater than −135° and less than−90°. That is, the angles of the alignment axis 49 formed with respectto the reference direction have two values (about 45° and −135°). Inthis embodiment, a rotational angle φ₀ of the alignment axis 49 of theliquid crystal layer 42 is assumed to have a value between the twovalues of the angles of the alignment axis 49 formed with respect to thereference direction, when the absolute value of the angle of thealignment axis 49 formed with respect to the reference direction is lessthan 90°.

In the first arrangement, the transmission axis 29 of the incident-sidepolarizing plate 25 is present between the range greater than −45° andless than 0° and the range greater than 135° and less than 180°. In thisembodiment, a rotational angle φ₁ of the transmission axis 29 of theincident-side polarizing plate 25 is assumed to have a value between thetwo values of the angles of the transmission axis 29 formed with respectto the alignment axis 49, when the absolute value of the angletransmission axis 29 formed with respect to the alignment axis 49 isless than 90°.

In the first arrangement, the transmission axis 33 of the wire gridelement 26 is almost parallel to the reference direction. In thisembodiment, a rotational angle φ₂ of the transmission axis 33 of thewire grid element 26 is assumed to have a value between two values ofthe angles (nearly 0° and nearly 180° in the first arrangement) of thetransmission axis 33 formed with respect to the alignment axis 49, whenthe absolute value of the angle of the transmission axis 33 formed withrespect to the alignment axis 49 is less than 90°.

In the first arrangement, the transmission axis 36 of the exit-sidepolarizing plate 28 is present between the range equal to or greaterthan 45° and less than 90° and the range equal to or greater than −135°and less than −90°. In this embodiment, a rotational angle φ₃ of thetransmission axis 36 of the exit-side polarizing plate 28 is assumed tohave a value between two values of the angles of the transmission axis36 formed with respect to the alignment axis 49, when the absolute valueof the angle of the transmission axis 36 formed with respect to thealignment axis 49 is less than 90°.

The contrast ratio CR is a ratio (T_(W)/T_(B)) of a lightness T_(W) of apixel at the lightest display (hereinafter, referred to as lightdisplay) to a lightness T_(B) of a pixel at the darkest display(hereinafter, referred to as dark display). The dark display is displaywhen the pixel value of 256 gray scales is 0. The light display isdisplay when the pixel value of 256 gray scales is 255.

The contrast ratio CR is the maximum value CR_(MAX) when the lightnessT_(W) of the light display is the maximum value T_(W) _(—) _(MAX) andthe lightness T_(B) of the dark display is the minimum value T_(B) _(—)_(MIN) at the rotation angle φ₀ of 45°, the rotation angle φ₁ of 0°, therotation angle φ₂ of 0°, and the rotation angle φ₃ of 90°. When thecontrast ratio CR is 80% or more of the maximum value CR_(MAX) in theprojector, it is difficult to recognize the deterioration in thecontrast ratio.

In the projector 1 according to this embodiment, the rotational anglesφ₁ to φ₃ are set with respect to the rotational angle φ₀ so that theabsolute value of the difference between the rotational angles φ₀ and φ₁is not 45° (where |φ₀−φ₁|≈45°, the lightness T_(W) of the light displaysatisfies Equation (4) below, and the lightness T_(B) of the darkdisplay satisfies Equation (5) below. Thus, in the projector 1, thecontrast ration CR can be set to be 80% or more of the maximum valueCR_(MAX), even when the lightness T_(W) is the minimum value (0.95×T_(W)_(—) _(MAX)) and the lightness T_(B) of the dark display is the maximumvalue (T_(B) _(—) _(M)IN):

0.95×T _(W) _(—) _(MAX) ≦T _(W) ≦T _(W) ≦T _(W) _(—) _(MAX)  (4), and

T _(B) _(—) _(Min) ≦T _(B)≦1.2×T _(B) _(—) _(Min)  (5).

In this embodiment, the rotational angle φ₂ of the transmission axis 33of the wire grid element 26 is set so that the rotational angle φ₀ ofthe alignment axis 49 of the liquid crystal layer 42 obtainable bymeasurement or the like satisfies Expression (1) below:

44°≦φ₀−φ₂<45° or 45°<φ₀−φ₂≦46°  (1).

The lightness T_(W) of the light display depends on a relation betweenthe rotational angle φ₁ of the transmission axis 29 of the incident-sidepolarizing plate 25 and the rotational angle φ₂ of the transmission axis33 of the wire grid element 26.

FIG. 5 is a distribution diagram illustrating a simulation resultobtained by varying the rotational angle of the transmission axis of theincident-side polarizing plate and the rotational angle of thetransmission axis of a wire grid element and examining a variation inthe lightness of light display. In the distribution diagram of FIG. 5,the lightness W of the light display is a value (T_(W)/T_(W) _(—)_(MAX)) obtained by normalizing the lightness T_(W) of the light displayby the maximum value T_(W) _(—) _(MAX).

As shown in the distribution diagram of FIG. 5, a contour of thelightness W of the light display has an elliptical shape having astraight line satisfying an equation of “φ₁=k1×φ₂” as a major axis. Theinventors have found out that the coefficient k1 is about 5.0 and therotational angle φ₁ of the transmission axis 29 of the incident-sidepolarizing plate 25 is sensitively changed with a change in therotational angle φ₂ of the transmission axis 33 of the wire grid element26. Based on the distribution shown in FIG. 5, it can be understood thatthe lightness T_(W) of the light display satisfies Equation (4) abovewhen the rotational angle φ₁ of the transmission axis 29 of theincident-side polarizing plate 25 satisfies Equation (2) below:

f1≦φ₁ ≦f2  (2),

where

-   -   f1=0.191×φ₂ ²+0.986φ₂−14.435 and    -   f2=−0.191×₂ ²+0.986×φ₂+14.435.

The lightness T_(B) of the dark display depends on a relation betweenthe rotational angle φ₁ of the transmission axis 29 of the incident-sidepolarizing plate 25 and the rotational angle φ₂ of the transmission axis33 of the wire grid element 26.

FIG. 6 is a distribution diagram illustrating a simulation resultobtained by varying the rotational angle of the transmission axis of anexit-side polarizing plate and the rotational angle of the transmissionaxis of a wire grid element and examining the lightness of lightdisplay. In the distribution diagram of FIG. 6, the lightness B of thedark display is a value (T_(B)/T_(B) _(—) _(MIN)) obtained bynormalizing the lightness T_(B) of the dark display by the minimum valueT_(B) _(—) _(MIN).

As shown in the distribution diagram of FIG. 6, a contour of thelightness B of the dark display has an elliptical shape having astraight line satisfying an equation of “φ₁=k2×φ₂” as a major axis. Theinventors have found out that the coefficient k2 is about 2.0 and therotational angle φ₃ of the transmission axis 36 of the exit-sidepolarizing plate 28 is sensitively changed with the change in therotational angle φ₂ of the transmission axis 33 of the wire grid element26 at sensitivity different from that of the rotational angle φ₁ of thetransmission axis 29 of the incident-side polarizing plate 25. That is,as shown in FIG. 4, when the transmission axis 29 is projected to theliquid crystal panel 27, the transmission axis 29 of the incident-sidepolarizing plate 25 is not necessarily perpendicular to the transmissionaxis 36 of the exit-side polarizing plate 28. Based on the distributionshown in FIG. 6, it can be understood that the lightness T_(B) of thedark display satisfies Equation (5) above when the rotational angle φ₃of the transmission axis 36 of the exit-side polarizing plate 28satisfies Equation (3) below:

g1≦φ₁ ≦g2  (3),

where

-   -   g1=0.064×φ₃ ³+0.841×φ₃ ³+1.525×φ₃ ³−1.46 and    -   g2=0.064×φ₃ ³−0.841×φ₃ ³+1.525×φ₃ ³+1.46.

FIG. 7 is a diagram illustrating a second arrangement of the opticalelements of the image forming system according to the embodiment.

In the second arrangement shown in FIG. 7, the rotational angle φ₀ ofthe alignment axis 49 of the liquid crystal layer 42 is set to be in therange greater than 0° and less than 45°. The rotational angle φ₁ of thetransmission axis 29 of the incident-side polarizing plate 25 is set tobe in the range greater than 0° and less than 45°. The rotational angleφ₂ of the transmission axis 33 of the wire grid element 26 is set tonearly 0°. The rotational angle φ₂ of the transmission axis 36 of theexit-side polarizing plate 28 is set to be in the range greater than 90°and less than 135°. In the second arrangement, the rotational angles φ₀to φ₂ are set so as to satisfy all Equations (1) to (3) above.

FIG. 8 is a diagram illustrating a third arrangement of optical elementsof the image forming system according to the embodiment.

In the third arrangement shown in FIG. 8, the rotational angle φ₀ of thealignment axis 49 of the liquid crystal layer 42 is set to about 45°.The rotational angle φ₁ of the transmission axis 29 of the incident-sidepolarizing plate 25 is set to be in the range greater than −45° and lessthan 0°. The rotational angle φ₂ of the transmission axis 33 of the wiregrid element 26 is set to be in the range greater than −45° and lessthan 0°. The rotational angle φ₃ of the transmission axis 36 of theexit-side polarizing plate 28 is set to be in the range greater than 45°and less than 90°. In the third arrangement, the rotational angles φ₀ toφ₃ are set so as to satisfy all Equations (1) to (3) above.

FIG. 9 is a diagram illustrating a fourth arrangement of the opticalelements of the image forming system according to the embodiment.

In the fourth arrangement shown in FIG. 9, the rotational angle φ₀ ofthe alignment axis 49 of the liquid crystal layer 42 is set to about45°. The rotational angle φ₁ of the transmission axis 29 of theincident-side polarizing plate 25 is set to be in the range greater than0° and less than 45°. The rotational angle φ₂ of the transmission axis33 of the wire grid element 26 is set to be in the range greater than 0°and less than 45°. The rotational angle φ₃ of the transmission axis 36of the exit-side polarizing plate 28 is set to be in the range greaterthan 90° and less than 135°. In the fourth arrangement, the rotationalangles φ₀ to φ₃ are set so as to satisfy all Equations (1) to (3) above.

In the projector 1 with the above-described configuration, therotational angles φ₀ to φ₃ are set so as to satisfy all Equations (1) to(3) above. Therefore, the lightness T_(W) of the light display satisfiesEquation (4) above and the lightness T_(B) of the dark display satisfiesEquation (5), the minimum value of the contrast ratio CR is 80% or moreof the maximum CR_(MAX). Accordingly, since the deterioration in thecontrast ratio can be suppressed so that an observer does not recognizethe deterioration in the contrast ratio, the projector 1 can display ahigh-quality image.

The deviation in the alignment axis 49 of the liquid crystal layer 42can be compensated by adjusting the directions of the transmission axis29 of the incident-side polarizing plate 25, the transmission axis 33 ofthe wire grid element 26, and the transmission axis 36 of the exit-sidepolarizing plate 28. Therefore, since the allowable range of thedeviation degree (error) of the alignment axis 49 of the liquid crystallayer 42, the yield ratio of the liquid crystal panel 27 can beimproved, thereby reducing the manufacture cost of the projector 1.

Since a displayed image is not rotated compared to a case where thedeviation of the alignment axis 49 of the liquid crystal layer 42 iscompensated by varying the position of the liquid crystal panel 27 withrespect to the other optical elements, for example, there is lownecessity to perform image processing or use an optical system tocompensate the rotation of an image.

The technical scope of the invention is not limited to theabove-described embodiments, but the invention may be modified invarious formed within the scope of the invention without departing fromthe gist of the invention. The requisites described in theabove-described embodiments may appropriately be combined. Further, atleast one of the requisites described in the above-described embodimentsmay be omitted.

In at least one of the three image forming systems, the rotational angleφ₀ of the alignment axis of the liquid crystal layer of the liquidcrystal panel, the rotational angle φ₁ of the transmission axis of theincident-side polarizing plate, the rotational angle φ₂ of thetransmission axis of the wire grid element, and the rotational angle φ₃of the transmission axis of the exit-side polarizing plate may be set soas to satisfy all Equations (1) to (3). For example, the aboveconditions may be satisfied in the green image forming system and theabove conditions may not be satisfied in at least one of the blue imageforming system and the red image forming system. Among the blue lightL1, the green light L2, and the red light L3, the green light L2 iscolor light which has the highest human visual sensitivity (the opticalabsorptance of human pyramidal cells). Therefore, the contrast ratio canefficiently be improved.

In the above-described embodiment, the illumination optical system 2 isconfigured to separate the white light emitted from the light sourcelamp 13 into three-color light and illuminate each color image formingsystem for each color light, but the invention is not limited thereto.For example, the illumination optical system may be configured toinclude a solid-state light source, such as a laser diode or alight-emitting diode, directly emitting each color light and toilluminate each color image forming system by each color light emittedfrom each light solid-state light source.

Further, the illumination optical system may be configured to include asolid-state light source emitting blue light or ultraviolet light and afluorescent body receiving the source light emitted from the solid-statelight source and to illuminate the image forming system by the lightemitted from the fluorescent body. In this configuration, theillumination optical system may be configured to combine the lightemitted from the solid-state light source and the light emitted from thefluorescent body and form the white light and to separate the whitelight into three-color light and illuminate each color image formingsystem for each color light. Furthermore, the illumination opticalsystem may be configured to separate the blue light emitted from asolid-state light source into a plurality of light fluxes by a halfmirror or the like and to illuminate the blue image forming system byone of the separated light fluxes and illuminate the other color imageforming systems by the light obtained by converging the colors of theother separated light fluxes by a fluorescent body.

In the above-described embodiment, a three-plate type projector has beendescribed. The above-described projector may be a single-plate typeprojector such as a field sequential type projector. The projectordescribed above in the embodiment may be used in a head-mounted display,a head-up display, and the like.

The entire disclosure of Japanese Patent Application No. 2011-064008,filed Mar. 23, 2011 is expressly incorporate by reference herein.

1. A projector comprising: an illumination optical system; anincident-side polarizing plate which is disposed at a position at whichlight emitted from the illumination optical system is incident andthrough which polarized light parallel to a transmission axis passes; awire grid element which is disposed at a position at which the lightemitted from the illumination optical system and passing through theincident-side polarizing plate is incident, through which polarizedlight parallel to a transmission axis passes, and from which polarizedlight perpendicular to the transmission axis is reflected; a reflectiontype liquid crystal panel which is disposed at a position at which thelight emitted from the illumination optical system and passing throughthe wire grid element is incident; an exit-side polarizing plate whichis disposed at a position at which light reflected by the wire gridelement in the light modulated and reflected by the liquid crystal paneland incident on the wire grid element is incident and through whichpolarized light parallel to a transmission axis passes; and a projectionoptical system which projects the light modulated by the liquid crystalpanel and passing through the exit-side polarizing plate, wherein inregard to an alignment axis parallel to a direction, in which a directorof a liquid crystal molecule in a liquid crystal layer of the liquidcrystal panel is projected to a surface perpendicular to a thicknessdirection of the liquid crystal layer, the transmission axis of theincident-side polarizing plate and the transmission axis of the wiregrid element which are projected to a reference surface perpendicular inthe thickness direction of the liquid crystal layer of the liquidcrystal panel, the transmission axis of the exit-side polarizing platewhich is projected to the wire grid element and is further projected tothe reference surface, a rotational angle φ₀ of the alignment axis ofthe liquid crystal layer from a reference direction parallel to thereference surface, a rotational angle φ₁ of the transmission axis of theincident-side polarizing plate from the reference direction, arotational angle φ₂ of the transmission axis of the wire grid elementfrom the reference direction, and a rotational angle φ₃ of thetransmission axis of the exit-side polarizing plate from the referencedirection satisfy all Equations (1) to (3) below:44°≦φ₀−φ₂<45° or 45°<φ₀−φ₂≦46°  (1)f1≦φ₁ f2  (2), where f1=0.191×φ₂ ²+0.986×φ₂−14.435 and f2=−0.191×φ₂²+0.986×φ₂+14.435, andg1≦φ₁ ≦g2  (3), where g1=0.064×φ₃ ³+0.841×φ₃ ³+1.525×φ₃ ³−1.46 andg2=0.064×φ₃ ³−0.841×φ₃ ³+1.525×φ₃ ³+1.46.